1. Field of the Invention
This invention relates to copolymers which, in addition to a cyclic imide structural unit, contain secondary, sterically substantially unhindered amino groups and to a process for the production of these products. The modified copolymers are produced by reaction of copolymers containing intramolecular carboxylic anhydride groups, more especially incorporated maleic anhydride groups, with certain primary/secondary diamines.
2. Description of the Prior Art
Previously, it was thought that the reaction between polyanhydrides and diamines containing primary or secondary, sterically unhindered amino groups led to crosslinked products due to the formation of polyimides or polyamides (cf. for example the relevant observations in DE-OS 3,024,525). This prior publication describes anhydride-functional polymers in which 67 to 95% of the anhydride groups are imidated with 4-amino-2,2,6,6-tetramethyl piperidine. According to DE-OS 3,024,525, the secondary amino group in this molecule is said to be sterically screened in such a way that it does not readily react with anhydrides so that, in the reaction of 4-amino-2,2,6,6-tetramethyl piperidine with polyanhydrides, only the primary amino group reacts with the cyclic imide.
The reaction of polymers and copolymers of maleic anhydride with diamines containing a primary or secondary amino group in addition to a tertiary amino group is known (DE-OS 1 570 594). In this case, the object of the reaction is to introduce tertiary amino groups which makes the polymers or copolymers soluble in aqueous acids. Since only one reactive amino group is present in the diamines, crosslinking reactions cannot of course take place during the modification.
It has now surprisingly been found that even diamines in which the secondary amino group is sterically hindered to only a minor extent, if at all, can be reacted with special maleic anhydride copolymers by a suitable process to form non-crosslinked polyimide copolymers containing free secondary amino groups.